1. Field of the Invention
This invention relates to a method of synthesizing carbon film and carbon particles by a vapor phase reaction.
2. Description of the Prior Art
Heretofore, diamond has been industrially applied to cutter and cutting tools because of its high hardness. Recently, however, many studies on the synthesis of diamond film have been carried out, since the diamond has not only good thermal conductivity but also has a possibility of preparing a semiconductor to provide a heat-resistant electronic device.
It is known that diamond can be synthesized not only at a high temperature under high pressure, but also its crystal can be grown under low pressure by using a gaseous carbon compound (see, for example, U.S. Pat. Nos. 3,030,187 and 3,030,188).
Only a diamond crystal smaller than that obtained in high pressure method is obtained by the low pressure method, but the low pressure method is attractive in the following reasons: firstly, it is possible to synthesize a thin film which may be utilized as a semiconductor; secondery, it is not difficult to introduce impurity elements to get the semiconductor. Recently, an excellent method using methane gas as a starting material was reported.
In order to obtain a carbon film as a semiconductor, however, it is necessary to prevent unforeseen impurities from being incorporated therein (the tendency is strong when the pressure is the reaction chamber is high) and to control a film thickness carefully.
Therefore it is preferable to synthesize the carbon film in a lower pressure. The pressure applied in the conventional method, however, is in the range of several to several tens of Torr, then the conventional method has a disadvantage in that it is impossible to stably produce the film under a pressure lower than that specified above.
We have made studies on carbon film expecting that a carbon film having a uniform structure (just as hydrogenated amorphous silicon has) can be satisfactorily utilized as a semiconductor material even if the film does not have a perfect diamond structure.